1. Field of the Invention
The present invention relates generally to engine analyzers having inputs from more than one remote device. More particularly, it relates to a circuit for automatically distinguishing among such remote devices.
2. Description of the Prior Art
As a result of both revolutionary advances in microelectronics and increased concern over automotive emissions, engine analyzers have become increasingly complex over the past several years. The latest generation of engine analyzers typically includes a number of input probes which connect to various parts of the engine and exhaust system to collect data, a microprocessor for analyzing the data gathered, and various input/output (I/O) devices for communicating with the user. The probes may include units for magnetic timing, for measuring current, for measuring pressure, for infrared analysis of the vehicle exhaust, and the like. The I/O devices may include keyboards, cathode-ray tubes, printers, teletypes, and the like.
With the large number of diagnostic probes now available for engine analyzers and the probability that new probes will be available in the future, it is common that the various probes be attached to the analyzer through one or more common connectors only when required by the particular diagnostic test being performed. A serious problem arises when the user connects the improper probe for the analysis desired. In most cases, the results of the analysis would so deviate from the expected that the user would realize his mistake. In the worst case, however, the information generated by the analyzer, while incorrect, would be within a reasonable range and the user would never know his mistake. For this reason, it is desirable that the analyzer be able to distinguish from among the various probes which might be connected thereto.
Similarly, the engine analyzer will be capable of operating with different I/O devices, any of which might be connected to the analyzer at a given time. It is desirable that the analyzer be able to identify which I/O device is connected to the analyzer and interface with that device in the appropriate manner.